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Author Topic: I stepped in it - XS750/896 build  (Read 3034 times)

Offline Pete12

  • Posts: 218
Re: I stepped in it - XS750/896 build
« Reply #10 on: Feb 05, 2018, 04:20:57 »
Hi Tom, the pilot and main jets are in the carbie bowls - the pilot is accessed from the inside and the main from the outside (underneath). It's not a bad idea as I guess you could change the mains without pulling the carbies off, but that can be verified by someone that owns one.

Offline XS750AU

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Re: I stepped in it - XS750/896 build
« Reply #11 on: Feb 05, 2018, 05:39:56 »
Hi Tom
Pete is correct, please refer to attached slides - it appears you unfortunately have Hitachi carbies. Unfortunate as it is supposed to be difficult to get spare parts and jets. As you have probably read most people get hold of a set of Triumph flat slide carbies which are very, very easy to convert over to operate on the XS triple engines. There are 2 brands of flatslides used on the triumph 900 triples, the first preference is the Kehin (Data Dave is using these)and the least favorite are the Mikunis (which I am using). The Mikunis are prone to wear.
Kehins appear to be more difficult to source as people keep hold of them!!!
Good luck.
“Engineering is the art of being approximately right rather than exactly wrong.”

Yamaha XS750-2D
Yamaha XS896
Husaberg FE550
Yamaha TT250
Yamaha IT200N

Offline datadavid

  • Posts: 1335
Re: I stepped in it - XS750/896 build
« Reply #12 on: Feb 05, 2018, 06:31:56 »
Yea, the keihins dont seem to wear out, easy to tune, plus they are the same carbs as on my thruxton so same parts everywhere. Somewhat expensive but can be found in bike breaker's. Mikunis suposedly had a problem with wearing slides and needle jets so triumph changed over to keihin.

Offline XS750AU

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Re: I stepped in it - XS750/896 build
« Reply #13 on: Feb 05, 2018, 07:05:16 »
Quote
Found a 1977 XS750
Looked at your carby photos again and I think you actually have Mikuni MK1 from the original 750, which are not much better than the Hitachi's. Same advice applies, get a set of Keihin Flatslides or failing that, Mikuni Flatslides (you can get parts to rebuild).
Cheers
“Engineering is the art of being approximately right rather than exactly wrong.”

Yamaha XS750-2D
Yamaha XS896
Husaberg FE550
Yamaha TT250
Yamaha IT200N

Offline Ryan Stecken

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Re: I stepped in it - XS750/896 build
« Reply #14 on: Feb 05, 2018, 09:37:18 »
I´ve had the same stock XS 750 carbies and switched to T300 Triumph Triple carbs from a Daytona 900.
Easy to clean, tune and no problems till now whatsover.
You only need to build yourself a choke lever and shorten the stock gas bowden.

Offline Integra99

  • Posts: 95
Re: I stepped in it - XS750/896 build
« Reply #15 on: Feb 05, 2018, 10:40:24 »

Done the same here.. Triumph Daytona carbs on mine too.. ran good straight out the box!

Offline teazer

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Re: I stepped in it - XS750/896 build
« Reply #16 on: Feb 05, 2018, 10:58:29 »
Tom, the pistons are not only oval but they are also tapered bottom to top.  The skirts cannot be machined to size in a lathe.  And the barrels cannot be successfully be bored on a mill or lathe.  They need to be done by an automotive machine shop with a rigid boring bar and correct hone.

Find a good automotive or motorcycle machine shop and take the new pistons and barrels and have them do what needs to be done.  You could also send them to someone like Bill Bune in Anoka MN.

The carbs  you have are Mikuni and are easy to work on.  Main jets are in the bottom of the bowls under the drain bolt and the pilot jets are in the top of the bowl.  There's a good article on the same design carbs at http://pinkpossum.com/GT750/carb/BS40carbs.htm

There are three types of Mikuni pilot jets and some BS series carbs use different ones.  MikeXS can supply the correct ones.

The three "vents" on top of the intakes look like vacuum ports to synch the carbs.  The one that has a hose on it was probably connected to the fuel tap to create the vacuum to open it.

Offline Frenchtom

  • Posts: 18
Re: I stepped in it - XS750/896 build
« Reply #17 on: Feb 09, 2018, 13:32:57 »
Hi Guys and thanks for the replies.  I have been out of town and unable to respond until now.  I was thinking of rebuilding the old Mikuni carburetors until I found these via google.  Are these the correct Mikuni flat slides?  They are the 38mm TM series.  They have my attention and I like the idea of parts availability. 

I came home to fresh pistons sitting in an unopened mail bag and have to say I am quite impressed with their craftsmanship.  I took some measurements and while no 2 are the same they are pretty close according to my calipers. 

I will try to remove the engine from the frame and split the case halves this weekend.  Stay tuned...



« Last Edit: Feb 09, 2018, 13:41:03 by Frenchtom »
1963 Honda Sport Cub
1977 Yamaha XS896

Billet: about as creative as duct tape

Offline XS750AU

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Re: I stepped in it - XS750/896 build
« Reply #18 on: Feb 09, 2018, 21:06:30 »
Hi Tom
Nanno (If you search you will find his blog on this site) used 3 x Mikuni TM carbies to work on his XS750 sidecar. I think they were 36mm, but it was a lot of work, a real lot of work!! You have to figure out how you are going to get 3 carbie cables going into 1 throttle cable. And then you have the issue of 3 individual chokes - how do you activate them. You can only reach 1 of the 3 choke plungers. It has been done but Nanno has put his TM carbies on the market and is now using others that are more simple.
If you get a set from a Triumph 900 triple they basically fit straight in.

The Cruising Image pistons are meant to be made in Japan not China, but who really knows, they are what they are. As long as you have them and give them to the shop that will bore the cylinders on a proper rigid set up there will be no problems.
“Engineering is the art of being approximately right rather than exactly wrong.”

Yamaha XS750-2D
Yamaha XS896
Husaberg FE550
Yamaha TT250
Yamaha IT200N

Offline XS750AU

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Re: I stepped in it - XS750/896 build
« Reply #19 on: Feb 09, 2018, 21:14:51 »
Tom
Here is the link to Nannos post with the TM carbies http://www.dotheton.com/forum/index.php?topic=74211
“Engineering is the art of being approximately right rather than exactly wrong.”

Yamaha XS750-2D
Yamaha XS896
Husaberg FE550
Yamaha TT250
Yamaha IT200N